The present invention relates to field of printers and other printing devices that output a hard copy document on a print medium, e.g., paper. More specifically, the present invention relates to a method and system of automatically sensing the size of paper or other print medium stored in a supply tray or area within a hard copy printing device.
Computers and computer networks are widely used by most all businesses to keep records, communicate, produce documents and otherwise manage information. Frequently, the work prepared on a computer is preferably rendered into hard copy form so that it can be stored or sent to another party. For this reason, printers and other printing devices that can render hard copy documents from computer data are critically important. Of equal importance are other printing devices that can be used to produce, copy or transmit hardcopy documents.
There are many different types of printers and printing devices. For example, types of printers include laser printers, inkjet printers, thermal printers, dot matrix printers and others. Other types of printing devices include, without limitation to, plotters, copiers, facsimile machines, multi-function peripherals, etc. As used hereafter and in the appended claims, the terms xe2x80x9cprinterxe2x80x9d and xe2x80x9cprinting devicexe2x80x9d will be used to refer expansively to all printers and printing devices that output hard copy documents on some form of print medium, including, but not limited to, the examples given above.
In addition to the wide variety of printers and printing devices as described above, there is also a wide variety of print mediums on which printing devices can print hard copy documents. Examples of print media include, but are not limited to, paper, adhesive labels, cardstock, vinyl, transparencies, etc. Each of these media may be of a different size that the others. Additionally, each type of print media may have one or several standard sizes that are available. For example, paper can come in several standard sizes including letter, A4, legal and others.
During the production of hard copy documents, by printing, copying, etc., it is extremely helpful, and sometimes essential, to determine the size of the print medium. For example, the user may require a particular size of print medium and may need to change the type of print medium in the printing device in order to produce documents on the desired size of print medium. Alternatively, there may be two or more different types or sizes of print medium stored in the printing device. If the user knows what size the various supplies of print media in the printing device are, the user can specify which size or type of print medium should be used for a particular printing job.
In another example, the job being printed may be too large for the size of print medium available to the printing device. In such a case, the user can change the size of print medium in the printing device or, perhaps, the printing device can scale the images being printed to fit the available printing medium.
In all these cases, it is advantageous or essential to determine the size of the print medium or media available to the printing device. It would be preferable for the printing device to be able to automatically determine the size of the print medium or media stored in the printing device so that the size information can be conveyed to a user or automatically taken into account by the printing device in scaling, orienting or otherwise manipulating images being printed.
In the past, complex mechanical systems have been proposed as means for automatically detecting the size of a print medium stored in a printing device. These system typically depend on monitoring the movement of adjustable guides within, for example, a paper tray of the printing device and determining the size of the print medium based on the movement of such adjustable guides activating switches that correspond to the position of the adjustable guides when accommodating standard sizes of print media.
These systems, however, are complicated and require moving parts that are susceptible to damage and disrepair. Additionally, prior art systems are only suited for detecting standard print medium sizes.
Consequently, there is a need in the art for an improved method and system of automatically detecting the size of a print medium in a printing device. Preferably, such an improved system would not rely on complex mechanical linkages and would be able to detect any size of print medium, whether a standard or custom size.
The present invention is directed to a system for automatically sensing a size of print medium available to a printing device. In one preferred embodiment, a system according to the principles of the present invention may include: a resonance chamber, a portion of which is open, wherein the open portion is partially covered by a supply of print medium; a sound emitting system for acoustically exciting the resonance chamber over a range of frequencies; a system for detecting a natural resonance frequency of the resonance chamber as partially covered by the supply of print medium; and a processor for determining a dimension of the print medium based on a relationship between the natural resonance frequency of the resonance chamber and the dimension of the print medium.
Preferably, the sound emitting system may include a speaker, and a variable oscillator driving the speaker over the range of frequencies. The sound emitting system may also include an amplifier for amplifying a signal from the variable oscillator to the speaker, and a current supply for supplying current to the amplifier.
The system for detecting the natural resonance frequency of the resonance chamber may include a current meter for monitoring the amount of current pulled from the current supply by the amplifier as the variable oscillator drives the speaker over the range of frequencies. In such a case the system for detecting the natural resonance frequency of the resonance chamber may include a processor which controls the oscillator to drive the speaker over the range of frequencies; receives an output signal from the current meter; and identifies the natural resonance frequency of the resonance chamber as a frequency at which the current meter signals a minimum of current being drawn by the amplifier.
Alternatively, the system for detecting the natural resonance frequency of the resonance chamber may include a transducer for monitoring the amplitude of sound waves excited in the resonance chamber by the sound emitting system. In this case the processor controls the oscillator to drive the speaker over the range of frequencies; the transducer sends an output signal to the processor that indicates to the processor when the amplitude reaches a peak; and the processor identifies the natural resonance frequency of the resonance chamber as a frequency at which the transducer signals the peak amplitude.
The present invention also encompasses methods of automatically sensing the size of print medium available to a printing device. As before, the method is preferably performed with a resonance chamber, which is open on a side that is partially covered by a supply of the print medium. Such a method may include the steps of detecting a natural resonance frequency of the resonance chamber as partially covered by the supply of print medium; and determining a dimension of the print medium based on a relationship between the natural resonance frequency of the resonance chamber and the dimension of the print medium.
The step of detecting the natural resonance frequency may be performed by acoustically exciting the resonance chamber over a range of input frequencies and then monitoring the amplitude of sound waves excited in the resonance chamber to identify an input frequency resulting in sound waves with a maximum amplitude. Alternatively, after acoustically exciting the resonance chamber, a method according to the present invention may involve monitoring current drawn by an acoustic system acoustically exciting the resonance chamber to identify an input frequency with a minimum current requirement.
The present invention may also be incorporated in a printing device, such as a copier or printer. The printing device may also include a supply tray for holding the supply of print medium.
The resonance chamber may be formed in the supply tray or, alternatively, in the feeder area of the printing device. If the resonance chamber is formed in the supply tray, the tray may further include an electrical interface between the supply tray and the printing device to connect electrical components of either the sound emitting system or the system for detecting the natural frequency of the resonance chamber which are also disposed in the supply tray.
Alternatively, if the resonance chamber is formed in the feeder, the supply tray may have a window in the bottom of the tray for allowing the supply of print medium to partially cover the resonance chamber formed in the feeder below the supply tray.